1. Field of the Invention
The present invention relates to semiconductor manufacturing apparatuses, and particularly to a semiconductor manufacturing apparatus having a nozzle with a plurality of tiny holes arranged corresponding to a plurality of semiconductor substrates disposed in a loader, and through which a reactant gas is supplied to each semiconductor substrate to form a desired layer on the substrates.
2. Description of the Related Art
As semiconductor devices become ever denser and smaller, the insulating layer of a capacitor, particularly in a DRAM (dynamic random access memory), has a trench (deep hole) with a higher aspect ratio (depth/width). Accordingly, known CVD (chemical vapor deposition) becomes unsuitable to form a uniform capacitor insulating layer in the trench with a high aspect ratio. In order to overcome this problem, atomic layer deposition (ALD) is increasingly carried out to form the insulating layer. ALD is a method for forming a desired film by depositing atomic layers on top of one another. For example, when a hafnium oxide (HfO) layer is formed on a semiconductor substrate placed at a constant temperature in a reaction chamber, a Hf source gas tetrakis (ethylmethylamino) hafnium (TEMAH, Hf(N(CH3)(C2H5))4) and an oxidizing agent ozone (O3) are alternately introduced. In this process, excess TEMAH is removed to prevent the reaction with ozone in a gas phase, by performing evacuation and inert gas purge between the steps of introducing TEMAH and ozone. The reaction of these gases inhibits atomic layer deposition and thus makes it difficult to form a uniform layer in the trench.
A series of six steps of TEMAH introduction, evacuation, inert gas purge, ozone introduction, evacuation, and inert gas purge forms a layer to a thickness of about 0.1 nm. For example, a 6 nm thick hafnium oxide insulating layer in a DRAM capacitor is formed by 60 series of these steps. For the formation of a uniform layer in the trench, each step requires at least 10 seconds. Therefore, the single series of the steps takes 60 seconds while 60 series takes 3600 seconds. Because of such a process time, it is quite difficult to ensure high productivity in a process using a sheetfed ALD apparatus, which treats semiconductor substrates one at a time.
In order to ensure high productivity in an ALD process, it is necessary to use a batch ALD apparatus which is capable of treating a plurality of semiconductor substrates at a time. For example, in case where 100 semiconductor substrates are treated under the above-mentioned conditions, a sheetfed apparatus requires about 100 hours, but a batch apparatus requires only 5 hours or less. The batch apparatus can treat 25 or more substrates at a time and is much superior in productivity.
FIG. 1 is a schematic representation of a known batch ALD apparatus used for forming a hafnium oxide layer.
The known batch ALD apparatus includes a reaction tube 101 defining a reaction chamber 102 and having an evacuation port 125 at its top. The evacuation port 125 is connected to a vacuum valve 127 with a joint 126. The vacuum valve 127 is connected to a pressure-regulating valve 128, and is further connected to vacuum pumps 130 and 131 through a vacuum pipe 129. In the reaction chamber 102, a boat 103 supported by a boat loader 126 holds a plurality of semiconductor substrates 104. The reaction tube 101 is provided with a heater 105 around the periphery to heat the semiconductor substrates 104. A hafnium source gas is introduced into the reaction chamber from a TEMAH source 112 through a TEMAH inlet valve 111, a liquid flow controller (for example, liquid mass flow controller, LMFC) 110, a vaporizer 109, a valve 108, an inlet pipe 107, and a nozzle 106 in that order. The vaporizer 109 is fed with nitrogen from a nitrogen source 115 through a flow controller (for example, mass flow controller, MFC) 114 and a TEMAH carrier N2 inlet valve 113. At the same time, the oxidizing gas, or ozone gas, is introduced into the reaction chamber from an oxygen source 120 through a flow controller (MFC) 119, an ozonizer 118, an ozone inlet valve 117, and a nozzle 116 in that order. The reaction chamber is purged with nitrogen gas introduced from another nitrogen source 124 through a flow controller (MFC) 123, a purge N2 inlet valve 122, and a nozzle 121 in that order.
The structure shown in FIG. 1 has been disclosed in Japanese Unexamined Patent Application Publication No. 6-275608, in FIG. 3. According to the structure shown in FIG. 1 or in an embodiment of this patent document, the TEMAH nozzle 106 is open in the vicinity of the bottom of the reaction chamber. In this event, TEMAH introduced through the TEMAH nozzle 106 is sufficiently supplied on semiconductor substrates placed at lower positions in the reaction chamber, but is insufficient for semiconductor substrates at higher positions. As a result, the thickness of the resulting hafnium oxide layer is seriously varied for the semiconductor substrates from the lowermost position to the uppermost position.
In order to overcome this disadvantage, as shown in FIG. 2, proposal has been made of an apparatus which has a nozzle extending to a higher position in the reaction chamber. This nozzle 106a has a plurality of tiny holes corresponding to the positions of the semiconductor substrates 104, and its end is closed with a clog 106b. This structure can uniformly supply a source gas to each semiconductor substrate. In this manner, the disadvantage can be overcome that the layers on the respective semiconductor substrates have thicknesses varying in the vertical direction of the reaction chamber. Japanese Unexamined Patent Application Publication No. 2004-23043, FIG. 1 has disclosed a similar structure.
An exemplary step in which the apparatus shown in FIG. 2 deposits a hafnium oxide layer will be described with reference to a deposition sequence shown in FIG. 3. In the sequence, the horizontal axis represents the elapsed time(s).
The semiconductor substrates are allowed to stand at 250° C. in the reaction chamber for the first 0 to 20 seconds. Then, the purge N2 inlet valve 122 is opened to introduce N2 to the reaction chamber. The reaction chamber is thus maintained at a constant high pressure.
In the next step, after 20 to 50 seconds from the beginning, on closing the purge N2 inlet valve 122, the TEMAH inlet valve 111 and the TEMAH carrier N2 inlet valve 113 are opened (with the valve 108 always open) to introduce TEMAH into the reaction chamber. At this stage, TEMAH is jetted through the tiny holes of the nozzle 106a and adsorbed at a level of atomic layer on the surface of the semiconductor substrate 104.
In the next step, after 50 to 70 seconds from the beginning, the TEMAH inlet valve 111 and the TEMAH carrier N2 inlet valve 113 are closed to stop the introduction of TEMAH so that the reaction chamber is evacuated. Thus, excess TEMAH remaining in reaction chamber is removed and the pressure in the reaction chamber is reduced to a low level.
In the next step, after 70 to 90 seconds from the beginning, the purge N2 inlet valve 122 is opened to purge the reaction chamber with N2 and to increase the pressure in the reaction chamber so that the reaction chamber is maintained at a constant high pressure. This step also contributes to the removal of the residual TEMAH from the reaction chamber.
In the next step, after 90 to 120 seconds from the beginning, the purge N2 inlet valve 122 is closed to stop the introduction of the purge N2, and besides the ozone inlet valve 117 is opened to introduce ozone into the reaction chamber. At this stage, the TEMAH deposited on the semiconductor substrate 104 is oxidized by the ozone into hafnium oxide at a level of atomic layer. The hafnium oxide has a thickness of about 0.1 nm, but is not in a form of film.
In the next step, after 120 to 140 seconds from the beginning, the ozone inlet valve 117 is closed so that the reaction chamber is evacuated to reduce the pressure in the reaction chamber to a low level. In the next step, after 140 to 160 second from the beginning, the purge N2 inlet valve 122 is opened to purge the reaction chamber with N2 and to increase the pressure in the reaction chamber so that the reaction chamber is maintained at a high pressure. Thus, a series of steps for depositing hafnium oxide is completed. This series is continuously repeated until a hafnium oxide layer is formed to a desired thickness.
Unfortunately, the apparatus having the nozzle with a plurality of tiny holes and the deposition using the apparatus have the following disadvantages.
Since the end of the TEMAH delivering nozzle shown in FIG. 2 is closed with a clog 106b, the residual TEMAH have to be removed through the tiny holes from the nozzle. It is however not easy to efficiently discharge the residual TEMAH from the nozzle. In the above-described deposition of hafnium oxide, the residual TEMAH still remains in the nozzle even if the steps of evacuating the reaction chamber and purging the reaction chamber with N2 are performed with TEMAH introduction stopped.
Consequently, the TEMAH remaining in the nozzle reacts with subsequently introduced ozone in a gas phase to produce hafnium oxide on the semiconductor substrates in the vicinity of the nozzle. Thus, the uniformity of the in-plane thickness of the resulting layer is degraded. Further, the resulting layer may not sufficiently coat the surface in the trench. Furthermore, hafnium oxide easily deposits in the nozzle, particularly around the tiny holes. The deposit may reduce the diameter of the tiny holes, or may peel off and adversely act as particulate matter.